I think there was a checkbox for joystick in the game options, but i may be wrong. If not, you should be able to disable it without physically disconnecting in its control software (if there is no any custom software, you can temporarily disable it in Windows Device manager).

While I don't have it in front of me I know there are settings for it in the player configuration files. Annul the binding values associated with that (they're pretty obvious) and that should do the trick also